High impact polyolefin compositions comprising e/p block copolymer and high density polyethylene

ABSTRACT

HIGH IMPACT STRENGTH POLYOLEFIN COMPOSITIONS FORMULATED OF 50% TO 98% BY WEIGHT POLYETHYLENE HAVING A SPECIFIC GRAVITY GREATER THAN 0.96 AND 50% TO 2% BY WEIGHT OF A SEQUENCED COPOLYMER FORMED OF 5% TO 50% BY WIEGHT OF A SEQUENCE OBTAINED BY STATISTIC COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH THE REMAINDER FORMED OF A PREVIOUS OR SUBSEQUENT SEQUENCE OF POLYMERIZED PROPYLENE.

United States Patent Othce 3,751,521 Patented Aug. 7, 1973 3,751,521 HIGH IMPACT POLYOLEFIN COMPDSITIONS COMPRISING Iii/l BLOCK COPOLYMER AND HIGH DENSITY POLYETHYLENE Iamurri Roger, Le Meyran, Martigues, France No Drawing. Continuation of abandoned application Ser. No. 811,595, Mar. 28, 1969. This application June 18, 1971, Ser. No. 154,675 Claims priority, application France, Apr. 17, 1968, 148,370 Int. Cl. CllSf 37/18 US. Cl. 260-876 B 10 Claims ABSTRACT OF THE DISCLOSURE High impact strength polyolefin compositions formulated of 50% to 98% by weight polyethylene having a specific gravity greater than 0.96 and 50% to 2% by Weight of a sequenced copolymer formed of 5% to 50% by weight of a sequence obtained by statistic copolymerization of ethylene and propylene with the remainder formed of a previous or subsequent sequence of polymerized propylene.

This is a continuation of copending application Ser. No. 811,595, filed Mar. 28, 1969, now abandoned.

This invention relates to high impact strength poly olefin compositions having high rupture strength and high fluidity for easy processing by conventional injection molding.

Polyethylene polymerization, with Ziegler type catalysts, is known to produce polyethylene polymers of relatively low molecular weight and having a high degree of crystallinity, suitable for use in injection molding. Such polymers are, however, unsuitable for use in a number of applications by reason of their relatively low impact strength.

It is known that polyethylene polymers of higher molecular weight give higher impact strength but that such increase in impact strength is usually accompanied by a decrease in fluidity, while in the molten state, such that the compositions are more difiicult to injection mold.

It is also possible to mix poor impact strength polymers with homopolymers or copolymers of olefins which are substantially amorphous and which are characterized by good elastic properties. Such mixtures have improved impact strength and improved fluidity but yield products which are fragile by reason of their poor elongation to rupture, especially at low temperatures.

It is also known to incorporate, with the polyethylene, a certain amount of sequenced copolymer of ethylene and propylene in which the sequences are produced alternately by homopolymerization of ethylene or propylene. The resulting compositions have a high degree of fluidity in their molten state, but their impact strength is no better than the polyethylene included within the mixture.

Attempts have been made to incorporate an amount of propylene into the polyethylene, but the polymers are not completely compatible such that the mixtures have different mechanical properties, especially poor elongation to rupture and low impact strength.

It is an object of this invention to produce and to provide a method for producing polyolefin compositions characterized by high impact strength, good elongation to rupture and high fluidity in the molten state.

It has been found that it is possible to incorporate into polyethylene certain sequenced copolymers, including one or two sequences obtained by polymerization of propylene and a sequence obtained by statistic copolym I erization of a mixture of ethylene and propylene, with the resulting mixture being characterized by unexpectedly high mechanical properties such as rigidity, impact strength, elongation to rupture, and fluidity in the molten state.

The invention comprises a composition formed of thermoplastic materials containing to 98% by weight of polyethylene, obtained in accordance with the well known Ziegler-'Natta process, using a Ziegler type catalyst, said polyethylene being characterized by a high specific gravity of more than 0.960 and 50% to 2% by weight of a sequenced copolymer of ethylene and propylene containing 5% to 50% by weight of a sequence obtained by statistic copolymerization of a mixture of ethylene and propylene containing approximately to by weight ethylene, said sequence being preceded and/or followed by a sequence obtained by the polymerization of polypropylene, and in which the sequence of statistic copolymerization of the mixture of ethylene and propylene preferably represents 10% to 20% by weight of the copolymer. The sequenced copolymer may also be produced by the now well known conventional Ziegler- Natta process, using a Ziegler type catalyst, as represented by US. Pats. No. 3,070,549, No. 3,113,115, No. 3,037,972 and No. 3,073,811.

The amount of statistic copolymer incorporated in the polypropylene depends somewhat upon the properties desired in the final composition. Increased amounts of statistical copolymer give increased impact strength but slightly lower rigidity.

In accordance with the practice of this invention, the mixture of polyethylene and sequenced copolymer can be easily efifected by conventional means, using conventional equipment for mixing plastic materials. For example, the materials can be mixed together while in the form of a powder and then combined by a kneading operation while heating to elevated temperature for reduction of the materials to a plastic or molten state, as by conventional mixing rolls, kneaders, Banbury or the like.

By reason of their high degree of fluidity, rigidity and impact strengths, the compositions of this invention find excellent use in the injection molding of large articles which require good rigidity and impact strength and which can be subjected to widely varying temperatures, as represented by dust bins, cartons, crates for the shipment of fruits and vegetables, bottle racks, etc.

In the following examples, the properties measured were determined by the following methods:

Fusion index was measured in accordance with ASTM 1238-52 T norm, in grams of material per 10 minutes, using a load of 2.160 kg. at a temperature of 190 C. with polyethylene and 230 C. with the copolymer and the various compositions under study.

Impact strength was measured in kg.cm./sq.cm. by

means of the Charpy notched impact test using a pendulum on a specimen in the form of a parallelepiped having a length of mm., a width of 10mm. and thickness of 4 mm. Use was made of a notch 4 mm. long and 2 mm. deep, set at an angle of 45 parallel to the thickness of the specimen in the axis of one of the faces measuring 120 mm. by 4 mm., with the pendulum strikin the specimen on the face opposite the notched face.

Bending strength was measured in kg./sq.crn. by means of the Dynstat apparatus of the Centre dEtude des Matieres Plastiques (Center for the Study of Plastics Materials).

The percentage of elongation to rupture was measured in accordance with R 527 norm.

Fluidity was measured by means of a Netstal injection press in which the composition being tested Was heated to a temperature of 225 C. and injected under a pressure of 865 bars into a mold in the form of a spiral maintained at a temperature of 25 C. The polymer enters the mold until it hardens and the spiral fluidity is the length in hum. of the resulting spiral of plastic material that is formed.

sequence representing the remaining 30% by weight of the copolymer.

The properties of the sequenced copolymer and the composition containing 90% of polyethylene are given 5 in the following Table II:

TABLE II Fusion Impact stren th Elongation to index (cm.kg./sq.cm. at- Bending rupture (percent) Spiral strength fluidity Composition 230 C.) 23 0. 0 C. (kg/sq. cm.) 23 0. 0 0. (mm.)

Sequenced copolymer 1. 3 35 15 450 600 300 460 Composition (polyethylene 90% copolymer 4. 8 12 6 550 1, 100 400 390 The following examples are given by way of illustra- 15 EXAMPLE 3 tion, but not by way of limitation:

EXAMPLE 1 A sequenced copolymer is prepared in accordance with a reaction comprising the following three phases: MlXlng 1S F mltlally Wlth matellals 1n the P Q First phase: Polymerization of propylene producing state and then in the molten state by means of a slubbing 2 a sequence representing 10% by weight f the total machine provided with a double screw, of 80 parts by polymen Weight of polyethylene ha ing a pe ific i y of -2 Second phase: Statistical polymerization of a mixture P p y the Zleglef P f P y Welght of ethylene and propylene producing a sequence repre- Of a sequenced copolymer Whlch 1S Obtalfled y a T636 senting 20% of the total weight of the copolymer, with tion carried out in the following manner: the percentage of ethylene units in this sequence being In a first phase, a mixture of ethylene and propylene 75% by weight. is polymerized to produce a sequence of statistic copolym- Third phase: Polymerization of propylene producing erization of ethyl ne and P py P t1ng15% y a sequence representing 70% by weight of the total Weight of the total sequence copolymer to be produced weight of the copolymer. and in which the percentage of ethylene units in the Two mixtures are prepared from the sequenced cosequence was approximately 70% by weight. polymer prepared as above and the polyethylene as in In a second phase, polymerization was continued with Example 1, the two mixtures representing approximately propylene until a copolymer is obtained which includes a and by weight of the sequenced copolymer sequence of homopolymerization of propylene representand 65% and 50% v by weight respectively of the polying the remainder of 85% by weight of the sequenced 3 ethylene. copolymer. The properties of the resulting compositions are given The constituents of the mixture and the resulting comin the following Table III:

TABLE III Fusion Impact stren th Elongation to index (cm.kg./sq.cm. at- Bending ruptnre,(percen t) Spiral strength fiuidit Composition 230 C.) 23 C. 0 C. (kg./sq. cm.) 23 C. 0 0. (mm.) s edc 1 er 1.2 22 415 700 a 0 5 lld i xt g (pol y e h y fine 50% copolymer 50%) 1. 6 4O 18 470 1, 000 880 $63 Mixture (polyethylene 65% copolymer 35%) 2 21 12 500 700 700 360 position have the properties given in the following 50 EXAMPLE 4 I Table I: A mixture is made in the same manner as Example 1,

TABLE I Impact strength (cm. Elongation to rupture kg./sq. cm.) at- V Btendhglg (percent) atflgpiiial 8 1'8 Composition Fusion index 23 0. 0 0. (kg/sq. 231.) 23 0. 0 0. (mm. Polyethylene having a specific gravity of 0.963..- e 6 (at 190 C.;. 3. 5 2 680 1, 200 300 360 sequenced copolymer 2 (at 230 40 15 425 900 600 4 0 Composition (polyethylene 80%, copolymer 20%)-.. 3 (at 230 C.)- 10 6 630 700 600 370 EXAMPLE 2 A mixture is made in the same manner as in Example 1 of 90 parts by weight of the same polyethylene and 10,

of parts by weight of the same polyethylene and 30% by weight of the sequenced copolymer obtained by the reaction comprising the following three phases:

First phase: Polymerization of propylene producing a sequence representing 20% by weight of the total weight I of the copolymer. I

Second phase: Statistic copolymerization of a mixture of ethylene and propylene producing a sequence representing 15 by weight of the total weight of the copolymer, the percentage of ethylene units in this sequence being 82% by weight. a a

Third phase: Polymerization of propylene producing a sequence representing 65 by weight of the total weight of the copolymer,

The properties of the sequenced copolymer and the of polyethylene compositions containing 70% by weight are given in the following Table IV:

6 in the,,combined sequenced copolymer contains 5% to 50% by weight of the statistical copolymer and combining the sequenced copolymer with polyethylene having TABLE IV Fusion Impact strength Elongation to index (cm. kgJsq. cm.) at- Bending rupture (percent) Sprlal (at Strength fluidity Composition 230 0.) 23 0. C. (kg/sq. cm.) 23 C. 0 C. (mnr) sequenced copolymer 0. 50 23 530 500 400 427 Mixture (polyethylene 70%, copolymer 30%) p 1. 2 25 550 900 700 370 I claim: i V

1. A composition of thermoplastic material consisting essentially of 50% to 98% by weight of polyethylene having a specific gravity of more than 0.960 and prepared by polymerization of ethylene in the presence of aZiegler type catalyst, and 2% to 50% by weight of a sequenced copolymerof ethylene and propylene comprising 5% to 50% by weight of a sequence obtained by statistic copolymerization of a mixture of ethylene and propylene containing ethylene units in an amount within the range of 60% to 85% by weight, said sequence being combined with a sequence obtained by the polymerization of propylene.

2. A composition as claimed in claim 1 in which the polymerizations are carried out in accordance'with the Ziegler-Natta process, using a Ziegler type catalyst.

' 3. A composition as claimed in claim 1 in which the sequence of polymerization of propylene precedes the sequence obtained by statistic copolymerization.

4. A composition as claimed in claim 1 in which the sequence obtained by the polymerization of propylene follows the sequence obtained by statistic compolymerizationQ 5. A composition as claimed in claim 1 which the sequenced copolymer contains 10% to by weight of the sequence obtained by statistic copolymerization.

6. Iniection molded articles produced by the composition of claim 1'; Y

7. In the method of producing a thermoplastic composition comprising producing a sequenced copolymer of ethylene and propylene by statistically copolymerizing a mixture of ethylene and propylene containing ethylene units in an amount Within the range of 60% to 85% by weight, polymerizing propylene in sequence and combining the sequence obtained by the polymerization of propylene with the sequence obtained by statistical polymerization of propylene and ethylene in the ratio wherea specific gravity of more than 0.960 and prepared by polymerization of ethylene in the presence of a Ziegler type catalyst to provide a thermoplastic composition consisting essentially of to 98% by weight of the polyethylene and 50% to 2% by weight of the sequenced copolymer.

8. The method as claimed in claim 7 in which the sequence of polymerization of propylene is carried out before the statistical copolymerization of ethylene and propylene.

9. The method as claimed in claim 7 in which the sequence of polymerization of propylene is carried out subsequent to the statistical copolymerization of ethylene and propylene.

10. The method as claimed in claim 7 in Which the sequence of polymerizing propylene is carried out both before and after the statistical copolyrnerization of ethylene and propylene.

References Cited UNITED STATES PATENTS 3,358,053 12/1967 Hostetler 260876 3,328,486 6/1967 Crawford et a1. 260876 3,487,128 12/1969 Okazaki et a1. 260876 3,627,852 12/1971 Aishima et al. 260-876 3,632,674 1/1972 Aishima et a1. 260-876 FOREIGN PATENTS 1,560,565 2/1969 France 260876 1,208,065 10/11970 Great Britain 260-876 MURRAY TILLMAN, Primary Examiner C. SECCURO, Assistant Examiner 7 US. or. X.R. 2s0 s7s B UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3,751,521

Dated August 7, 1973 Inventor(s) Roger IAMURRI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, in Table II, column "Impact Strength", at 0C,

line 2 delete "6" and insert therefor 5 Signed and sealed this end-da of April 197M.

(SEAL) Attost:

EDWARD M'.FLETCHEH,JR. c. MARSHALL D MN Attesting, Officer Commissioner of Patents 

